Conventionally, when an SiC substrate/SiO2 insulating film interface in a MOSFET using a semiconductor SiC is generated, the surface of the semiconductor SiC substrate is hydrogen terminated, and the surface is oxidized, or an insulating film is deposited, so that the SiO2 insulating film is formed. At this occasion, the hydrogen termination of the SiC substrate surface is easily detached, and oxygen enters into the inside of the substrate to oxidize the substrate.
The SiC substrate surface is considered to be oxidized as follows. Oxygen enters into the bond between Si—C in proximity to the surface, and this forms oxygen coordinated with the bond between the two. At this occasion, there are many bonds at the back side of elements of the outermost surface (which will be referred to as back bonds), and accordingly, oxygen randomly enters in proximity to the surface or in a depth direction, to make the interface rough as it is oxidized. As long as oxygen exists, this is inevitable, and the interface starts to become rough as soon as the SiO2 insulating film is formed. Further, in the SiC substrate, carbon atoms are discharged as such forms as CO, so that the carbon atoms are diffused in the SiO2 insulating film. As described above, when the oxidized film is formed directly on the hydrogen-terminated SiC substrate as in conventional techniques, the following three problems occur: (1) the surface is made into rough, (2) the interface dangling bond increases, and (3) diffusion of substrate constituting carbon into the insulating film. These three problems occur not only when SiO2 film is formed but also when oxide insulating films (for example, Al2O3, HfO2, HfAlO) and oxynitride insulating films (for example, AlON, HfSiON) are formed. This problem occurs when the hydrogen termination is detached from the SiC surface to activate the SiC surface, and oxygen reaches such activated SiC surface.